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Knee Joint
Knee joint is the largest and most complex joint. It is a hinge joint between the femoral condyles, patella and the tibial plateau. Motion: * Flexion: posterior surfaces of femoral condyles articulate with posterior tibial condyles * Extension: femoral condyles roll forward on tibial condyles and menisci and the patella rises. At the final 30 degree, the femur slides and rotate internally to lock * Initiating flexion from fully extended knee ** Requires lateral.external rotation of the femur produced by popliteus ** "Unlocks" joint, allowing remainder of motion to take place Extensor Mechanism * Quadriceps tendon converges on patella * Fibers of rectus femoris course over patella to form inferior patellar tendon * Fibers of vastus lateralis and medialis contribute to lateral and medial retinacula, respectively Muscles: * Extensors: Four parts of quadriceps femoris ** Rectus femoris, vastus lateralis, vastus medialis and vastus intermedius * Flexors ** Hamstrings: Biceps femoris, semitendinosus, and semimembranosus ** Sartorius, gracilis ** Popliteus (arises as tendon from popliteal groove at lateral femoral condyle, inserts onto posterior surface tibia; flexes knee and medially rotates tibia at beginning of flexion. Nerves of knee joint * Femoral nerve supplies ** 3 branches, one to each of the vasti, and to anterosuperior part of joint ** Largest is nerve to vastus medialis which accompanies descending genicular artery * Common peroneal nerve ** Superior lateral genicular nerve ** Inferior lateral genicular nerve ** Recurrent genicular nerve * Tibial nerve ** Superior medial genicular nerve ** Middle genicular nerve ** Inferior medial genicular nerve * Obturator nerve: Sends a genicular branch through adductor magnus to join popliteal artery, running to posterior aspect of joint Blood supply * Popliteal artery supplies 5 genicular branches * Anterior tibial artery supplies 2 recurrent branches * Femoral artery supplies descending genicular branch * Lateral circumflex artery supplies descending genicular branch Bony features: * Medial femoral condyle larger than lateral * Intercondylar notch accommodates cruciate ligaments * Anteriorly, trochlear groove accommodates patella and is generally V-shaped Cartilage * All the surfaces contains cartilage * Patella cartilage is the thickest in the body 3-4mm. Patella: triangular sesamoid bone, wider at the anterior base. * Articular surface divided by vertical ridge into lateral and medial facets Articular Capsule * The knee capsule is a dual-layered structure that surrounds the knee joint. It is thickened laterally by the collateral ligaments. ** Outer layer is fibrous connective tissue ** Inner layer is synovial membrane which secretes synovial fluid and provides lubrication. ** Femoral boundaries: *** proximal femoral condyles *** intercondylar fossa posteriorly *** patellar retinaculum anteriorly *** articular margin of the femur medially ** There is no capsule above the patella, allowing the suprapatellar bursa to communicate with the joint. ** Tibial boundaries: *** the tibial condyles posteriorly and medially *** patellar retinaculum and tibial tuberosity anteriorly *** head of the fibula laterally ** There is also an aperture for the popliteus tendon at the lateral tibial condyle. Menisci: Two pads of cushion fibrocartilage, that lubricate, and stabilize knee. * Attached by anterior and posterior roots to tibial surface * Medial aspect attached to capsule throughout extent * Lateral aspect attached to capsule at anterior horn and far posteriorly, but by fascicles to popliteus at body and posterior horn Cruciate ligaments * Intra-articular but extrasynovial * Major stabilizing structures to anteroposterior motion * ACL originates at posterolateral intercondylar notch, crosses anteromedially, and inserts at medial tibial spine/tibial surface * PCL originates at mid medial intercondylar notch, crosses posteriorly and slightly laterally, and inserts extra-articularly at posterior center of tibia below joint line. Medial Supporting Structures * Superficial (layer 1) ** Pes anserinus: Anteromedial tibial insertion *** Sartorius embedded in crural fascia *** Gracilis immediately deep to sartorius *** Semitendinosus immediately deep to gracilis * Middle (layer 2) ** Superficial medial collateral ligament (longitudinal and oblique components) *** Origin medial epicondyle; runs slightly anteromedially to insert on tibia 5 cm distal to joint line *** Anteriorly, longitudinal component fascia blends with layer 1 *** Posteriorly, oblique component blends with layer 3 as posterior oblique ligament * Deep (layer 3) ** Capsular layers (sometimes termed deep fibers of MCL) at mid portion of knee *** Meniscofemoral ligament *** Meniscotibial (coronary) ligament ** More posteriorly, superficial MCL blends with capsular layers MCL ** Posterior oblique ligament arises from superficial MCL *** Blends with posteromedial meniscus *** Receives fibers from semimembranosus tendon *** Envelops posterior aspect femoral condyle, termed oblique popliteal ligament Lateral Supporting Structures * Superficial (layer 1) ** Iliotibial band anteriorly, inserting on Gerdy tubercle ** Superficial portion biceps femoris posterolaterally, inserting on fibular styloid * Middle (layer 2) ** Quadriceps retinaculum anteriorly ** Posteriorly, 2 ligamentous thickenings which originate from lateral patella * Deep (layer 3): Several thickening in lateral part of capsule function as discrete structures ** Lateral (fibular) collateral ligament originates lateral femoral epicondyle, extends posterolaterally to insert on lateral fibular head ** Arcuate ligament originates from styloid process fibular head, interdigitates with popliteus, and inserts into posterior capsule near oblique popliteal ligament Variant: * Meniscus ** discoid menisci ** circular menisci ** meniscal transverse ligament * Cruciate ligament ** Accessory slips of ACL * Patella ** discoid patella